Hardware, such as electrical equipment with digital components, often requires the setting or resetting of internal logic states. For example, during the initial energization or power-up sequence of electrical components, such as discrete gates or more complete integrated circuits, the logic states of those components must be set or reset to defined levels. This reset sequence is required to ensure that the components will function properly and as expected. In this manner, other system components, such as other gates or processors, can properly assume the startup state of the components.
Reset circuits can be used to reset electrical components. Reset circuits typically consist of simple resistor-capacitor (R-C) networks connected to a reset pin of each integrated circuit (IC). The reset circuits typically provide a reset pulse to each of the ICS via each IC's reset pin.
For example, FIG. 1A is a schematic view of a prior art reset circuit for resetting an IC 102 such as a microprocessor. The reset circuit includes resistor 108 and capacitor 106. Resistor 108 is electrically connected to power input VCC 110 and to reset input 104 of IC 102. Capacitor 106 is also electrically connected to reset input 104, as is also electrically connected to ground 112. Power input VCC 110 is electrically connected to the IC's VCC input 114, and IC 102 is also electrically connected to ground 112.
FIG. 1B shows another prior art example of a reset circuit for resetting an IC 102. Similar to FIG. 1A, FIG. 1B includes resistor 108 and capacitor 106. FIG. 1B, however, also includes diode 116, which as shown is electrically connected in parallel with resistor 108. As indicated in the figure, reset input 104 of IC 102 is electrically connected to diode 116, resistor 108, and capacitor 106.
FIG. 2 shows yet another prior art example of a reset circuit. In this example, IC's 202 input VDD 216 is electrically connected to power input VDD 214. In addition, reset signal 218, which is electrically connected to reset input 218 of IC 202, is also connected to various other components of the reset circuitry including resistor 206, capacitor 208, diode 204, and inductors 210 and 212.
The prior art reset circuits of FIGS. 1A, 1B, and 2 include R-C networks with R-C time constants that, by changing the values of the R-C components, can be adjusted to provide a variable time period for reset activity to stabilize. Under normal (e.g., ideal) operating conditions, these circuits tend to work well. Under abnormal conditions, such as conditions with power transients, power interruptions, switching transients, or even brown-out conditions, however, these circuits behave differently and can negatively affect the logic states of logic gates within the digital devices (e.g., IC 102, 202). For example, these prior art reset circuits do not compensate for power transients during power-up, thus potentially leaving logic gates in unknown states at startup.